Wire conveyor belt systems are widely used in a great variety of industrial fields. A wire mesh overlay generally comprises the support surface of a wire conveyor belt, with the mesh overlay being formed of wire spirals intermeshed together by connecting rods which extend transversely across the width of the belt. Typically spiral overlays are comprised of interconnected flat spirals intermeshed and connected to one another by the rods. The ends of the rods are inserted into connective links which may also serve as tractive links around a sprocket wheel.
One of the problems associated with a conventional spiral overlay is that generally the spirals have been designed without any provision for controlling the pitch of the spirals as the overlay winds around the sprocket wheel or around a turning section of the conveyor. The pitch is defined to be the distance between adjacent rods of a conveyor overlay. In operation, the pitch decreases when traversing a sprocket wheel on a straight run of a conveyor, and the pitch will vary along the width of the overlay as an overlay winds around a turning section or curve of the conveyor. Varying pitch is also experienced in the transition section of a conveyor between a straight run and curved portion. Whenever the pitch varies, however, without significant pitch control, adjacent spirals bunch up and causes the leading edge of one spiral to be vertically displaced from the trailing edge of an adjacent spiral. This displacement results in rippling of the overlay and misalignment of the spirals, and can lead to permanent distortion if the spirals are subject to bending and twisting stresses beyond their elastic limit.
U.S. Pat. No. 3,920,117 to Roinestad and U.S. Pat. No. 4,878,362 to Tyree, Jr. exemplify previous attempts to provide some measure of pitch control to spiral overlays. Both the Roinestad and Tyree patents provide spirals having upward indentations on their undersides to contain the rods in bent wire portions. Although the indentations may prevent some displacement of the rods toward each other, the bent wire portions do not provide as positive a pitch control as the elongated loops of the present invention which completely contain the rods therein and completely prevent the rods from touching each other. In contrast, the bent wire portions of the prior an spirals do not prevent the rods from touching each other entirely, especially in jam situations, the bending and twisting forces in the belt would still cause the rods to travel together and result in all loss of pitch control. Furthermore, forming indentations on each turn on the underside of the spiral is costly, difficult and involves more manufacturing steps, especially when using high tensile wire.
Another problem associated with the use of a conventional spiral overlay is that generally no provision is made to prevent conveyed items from slipping on the support surface while the overlay traverses inclined portions of the conveyor. Prior attempts at solving the problem typically involved an additional manufacturing step. One of the ways was to fasten clips onto a completed overlay by crimping or welding. Another way was to rigidly attach solid bars or plates which traverse the overlay using screws. Extra attachment steps such as these result in higher cost and lower efficiency. Thus, there has been a need for an economical way of providing lift elements for added traction on the conveying surface of the overlay to prevent conveyed items from falling down an inclined section and bunching up on one portion of the overlays.
In addition, when conveying small articles or articles that move about easily, there has been a need to provide edge guards along the side edges of the overlay in order to prevent the items from falling off of the conveyor altogether. Edge guards have also been provided in the past by rigidly securing plates to the overlay which also involved the extra step of attachment during manufacture. For articles which are measured or separated prior to loading onto the conveyor, there has been a need to divide the support surface of the overlay into pockets to contain and convey premeasured quantities of articles or separated articles.